1. Field of the Invention
The present invention relates to an ink-jet recording apparatus, and a recording control method for the ink-jet recording apparatus. More particularly, the present invention relates to a dot-matrix ink-jet recording apparatus that records an image by ejecting ink at a plurality of ejected ink amounts of the same color ink, each value of n-level quantized data (n is equal to or greater than 3) corresponding to a respective ink ejected amount and each value expanded in a matrix of L columns by M rows for each of the plurality of ink amounts of the same color.
2. Description of the Related Art
Many efforts have been made for high-resolution images by using smaller recording liquid droplets in ink-jet recording apparatuses. In one proposed recording apparatus, ink of the same color is ejected at a plurality of amounts to form an image to satisfy both a high-definition requirement and a high-speed recording requirement.
Japanese Patent Laid-Open No. 2002-301815 discloses an ink-jet recording apparatus. In this ink-jet recording apparatus, record data corresponding to a plurality of recording elements different in the size of forming dots is generated, and the generated record data for the plurality of dots different in size is independently converted with respect to one pixel. The conversion process here refers to a relatively low resolution and multi-level quantization process that is performed by a host apparatus. Image data subjected to the conversion process is transferred to the recording apparatus. The recording apparatus then converts the received low-resolution and multi-level quantized data to a dot pattern of a predetermined matrix. The recording apparatus performs a so-called dot-matrix recording by recording the data in the dot pattern.
Several techniques have been proposed in connection with the recording method using dot matrix. In one technique, a plurality of dot matrices different in dot pattern are prepared beforehand, and a dot matrix is selected from among the plurality of dot matrices according to a random number having a predetermined number of bits, and is then assigned to the record data. In another technique, the presence or absence of data in a raster is identified, and the dot patterns are successively switched.
It is found that the dot patterns assigned to each of the plurality of dots different in size cause the following problem depending on the layout of the dot patterns.
An error in the landing of ink droplets, the sheet conveyance in the recording apparatus, and the scanning of a carriage may cause periodic density non-uniformities and streaks on an actual image in which the same tonal gradation continuously extends.
The periodic non-uniformities and streaks are closely related to a dot coverage ratio per unit pixel, namely, a so-called area factor per unit pixel. If dots different in size are placed in the same pixel in an overlapping manner with an image output in an intermediate gradation region, the area factor gets smaller than in the case where the dots are separately placed, and the density non-uniformities and streaks become pronounced.
If horizontally aligned recording heads for projecting ink droplets of a plurality of colors are used, dots different in size or different in color may be placed in an overlapping position along the same path. A recording medium fails to fully absorb ink in a localized area. The dot is deformed in shape, thereby becoming a noise-like image not preferable in the image formation.